1. Field of the Invention:
The invention is in the field of bone prostheses.
2. Description of the Prior Art:
In the past, various hinge-like prosthetic joints have been disclosed which comprise a pair of pivoted members fastened together by some type of pin. Examples of these pinned joints include U.S. Pat. Nos. 3,772,709 to Swanson; 3,656,186 to Dee; 3,765,033 to Goldberg et al.; 2,696,817 to Prevo; and 3,466,669 to Flatt.
Ball and socket joints for providing a primarily hinge-type motion are shown in U.S. Pat. Nos. 3,694,821 to Moritz and 3,506,982 to Steffee. The Steffee joint is intended primarily for fingers and the two components of the joint are assembled through a snap-in fit along a line more or less colinear with the direction of orientation of the stems of the joint components when the finger is in its straight or extended position. Another somewhat similar joint is shown in U.S. Pat. No. 3,760,427 to Schultz. In the Schultz joint, the ball of the ball-and-socket arrangement is inserted into the socket member from a direction above the socket in a line which lies within the plane of pivotal motion between the two joint members. Subsequent to this insertion of the ball into the socket, the socket member is inserted further into the receiving bone to cover the opening through which the ball is inserted.
In a joint of the type above described wherein the insertion of the ball into the socket is more or less direct or in a straight line with the extended position of the joint, the joint is subject to forces opposite to those necessary for insertion along this same line. In such a joint there also is a considerable freedom of movement in lateral directions as well as along the main direction of hinge-like motion between the joint components, and this can be a disadvantage especially in the case of an arthritic hand wherein the joints are subject to lateral forces; the joint would be more advantageous if resistant to these lateral forces. The insertion of the ball member into the socket of the socket member, such as described in the Schultz patent, provides an additional implantation step due to the necessity of a second stage of insertion of the socket member further into the bone after assembly.